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seemed therefore of interest to determine the threshold of local discrimination for a pure tone of deep pitch. For if this threshold should prove to be of approximately the same magnitude as that for tones of higher pitch, that would support the view that localisation depends in both cases on the same condition of stimulation, namely difference of intensity of stimulation of the two nerves; whereas if the threshold for deep tones should prove to be of a very different order of magnitude from that of higher tones, that result would support Lord Rayleigh's interpretation. Owing to a variety of difficulties and the departure of one of us from England for an indefinite period, we were able to make only one satisfactory determination of a threshold for a pure tone of deep pitch. We used a fork of frequency 100, and a cylindrical brass resonator. By bowing the fork gently we produced a note which was quite inaudible to the subject at a distance of one metre, until the fork was held close to the mouth of the resonator, when the deep tone appeared to be free of overtones. Proceeding as in the first series, we determined the threshold at position A for one subject (W. McD.) and found that 25° is approximately the measure of it. The subject made his judgments with great uncertainty in all cases—owing perhaps to the very unfamiliar character of the tone; and this made it difficult to determine the threshold with accuracy; but it was quite clear that its value lies between 20° and 30°. The corresponding threshold of the same subject for the pure tone of higher pitch was 20°—. It would seem, then, that the thresholds for the pure tones of high and of deep pitch do not differ very greatly, but are of the same order of magnitude.

In conclusion we would venture some remarks on the bearing of our results upon the second of the two problems distinguished above, namely the problem of the way in which the operative conditions of stimulation are utilised in the formation of the judgment of direction.

We would insist upon a difficulty that has been, we think, too little regarded by those who have accepted difference of intensity of stimulation of the two ears as a principal condition of localisation. Lord Rayleigh has calculated the approximate intensity of the sound-shadow thrown by the head when a note of medium pitch is sounded at one metre from the head1. This shadow is the measure of the difference of intensity of stimulation of the two ears, when the source of sound lies at one side of the head in the line of the interaural axis. It would seem that the difference must, even in the case of tones of medium pitch, be very considerably less than 30 °/0 of the total intensity, which is usually accepted as the approximate measure of the threshold of discrimination of intensity of sound. Our experiments (Series 1) show that in the case of pure tones (when apparently difference of intensity is the sole condition of discrimination) the position of a source of sound is perceived to be changed when it is moved some 20° only from the sagittal plane. The change in the intensity of the sound-shadow produced by such a change of position is, we imagine, very much less than the total value of the sound-shadow. It would seem then that the least difference of intensity of stimulation of the two ears that can determine judgment of direction is very much smaller than the least difference of intensity that can be appreciated as such. It is in accordance with this fact that the subject was not aware of hearing the pure tone with both ears, and of inferring its position from the greater intensity of the tone in one ear; but usually simply heard the one tone there or there. Occasionally it happened that the subject's answer was arrived at by way of an inference from an awareness that one ear was more strongly stimulated than the other, but in such cases this awareness seemed due to skin-sensation, or at least to sensation localised distinctly in the meatus of the more strongly stimulated ear. It seems necessary then to postulate some local signature of the tone-sensations determined by the unperceived difference of intensities of the stimulations of the two ears; possibly some reflexly evoked tendency for the face or the eyes to be turned to the source of sound, as suggested by Mr Matsumoto1. Such a theory of local signature seems strictly analogous to Lotze's doctrine of visual local signs, but escapes its greatest difficulties, because it has to deal with the localisation in one direction only at any one moment, and not with a sum of directions constituting an extended surface'. We venture to suggest also that such a theory might be rendered more acceptable, if we allow the local skin-sensations of the meatus to cooperate with movement-tendencies in the constitution of the local signs. Thus we should have a simple system of complex local signs comparable to the complex visual local signs of Prof. Wundt's theory.

1 Nature, Vol. Lvi. J. of Psych, Ii 26

1 'Researches on acoustic space,' Studies from the Yale Psychological Laboratory, Vol. Y. 1897.

* Von Kries [Ztschr. f. Psychol, u. Physiol, d. Sinnesorg., Bd. i.) has argued that such a theory is unacceptable because he found it possible to localise correctly two simultaneously sounded whistles of different pitch on the left and right sides respectively. To us it seems that no difficulty is presented by this fact, unless the two sounds are not only simultaneous but also of minimal duration.

A di6Sculty for any theory is presented by the fact that the surprisingly accurate discrimination of the positions of noises and complex tones seems to be due to the cooperation of two or more conditions, each of which alone renders possible only an inferior degree of accuracy. This effective cooperation or summation of the two or more favouring conditions seems to us a very remarkable fact, and one very difficult to understand.

THE 'PERCEPTIVE PROBLEM' IN THE AESTHETIC
APPRECIATION OF SINGLE COLOURS.

By EDWARD BULLOUGH.
[From the Psychological Laboratory of Cambridge.']

I. The Object: the 'Perceptive Problem'; the 'Aspects ofColour';

'Perceptive Types.'
II. Experiments: Purpose, Material and Methods, Defects, Results.
III. Analysis of Records: A. the 'Aspects of Colour.'

B. the 'Perceptive Types'
IV. Conclusion: the Aesthetic Values of the 'Perceptive Types'

I. The Object.

The object of this set of experiments is the investigation of a problem of colour-appreciation, more fundamental than the barren question whether certain colours are per se and universally pleasing, and more fundamental than the investigation into the part which tone, saturation and luminosity play in colour-preferences. For the problem is one which in the case of all aesthetic objects, not only of colours, lies at the bottom of, and conditions, our appreciation of them. It is what may be called the 'perceptive problem.'

It appears that J. Segal1 was one of the first definitely to call attention to the importance of this point, as a phase antecedent to the aesthetic contemplation. In his experiments with simple spatial forms he notices that the appreciation of an oblique straight line fluctuated according as the line was taken either as a badly drawn vertical or horizontal, or as representing the movement of the line to lift itself up to a vertical position or as flying along like an arrow. He observed

1 J. Segal, 'Uber die Wohlgefalligkeit einfacher ranmlieher Formeii,' Arch, fiir d. grs. Ptychol. 1906, Bd. vn. S. 107.

these differences in the perception of the line both between different persons and in the same person at different times, and he lays special stress upon the obvious connexion existing between this initial perception and the ultimate appreciation of the object. This is a fact which obtains in our appreciation of other things as well, and the tendency to regard an object as 'meaning' one thing rather than another, cannot fail to produce divergencies in the attitude and appreciation of different subjects. It is true that in certain objects, e.g. those of Fine Art, the perceptive differences are far subtler and possibly much smaller than in the case of a straight line, since the very complexity of such objects stands in the way of considerable perceptive differences. Thus the mere addition of an arrowhead to the oblique line would at once have rendered Segal's figure quite unambiguous, and the human significance of statuary and painting still further minimises perceptive multiformity, though it opens the gate to other more complex factors of appreciation.

In the case of colours this perceptive problem appears of paramount importance for two reasons. First, because the 'cognitive' value of colour is very low, and secondly, because it possesses a peculiarly high suggestive power which is only rivalled by odour in diversity and precision. Consequently a colour presents at once too few and too many indications to perception: any interpretation or meaning within the widest limits of fancy becomes possible. A colour may, therefore, 'mean' almost anything; experience seems to show that for no two persons does it carry exactly the same import; and it is consequently impossible to straightway coordinate the experiences of different subjects (though they are induced by one and the same object), simply because the colour already stands to the individuals for entirely different things, before any effects of like or dislike appear. Expressed in a general way, the perceptive problem in the aesthetic appreciation of single colours means the problem of the differences existing in the perception of single colours, in so far as such perceptive differences condition differences of aesthetic effect.

Translating this subjective formulation of the problem into the corresponding objective form, the question deals with what might be called the 'aspects of colour.' What, for example, strikes one person, is the softness or brightness of a colour, or its 'objective' qualities; what appeals to another is its associative import. These are only two aspects; and the object of these experiments is in the first place to investigate what aspects actually occur in colour-appreciation, and to

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